More than any other factor, lack of intelligence, aptitude, training and experience make this situation.
When I served in the US Army 44 yrs, ago, my boss, a Warrant Officer, said he'd gladly have a blacks in his small technical group, if they were qualified. He said none had yet been qualified.
Few blacks go to college and tackle difficult subjects. Math, science, engineering, etc.
The Hermann Cains, Thomas Sowell's and Ben Carson's are exceptions, not the rule.
OTOH medicine is full of Asians.
Asian mean IQ 106, black mean IQ 85.